Antenna (radio)

Antenna

Multiple patch (rectangular) antennas found atop a Cellular Tower
Working principle‍	Electromagnetic radiation
Invented	Heinrich Hertz
First production	1886
Electronic symbol

In radio engineering, an antenna (American English) or aerial (British English) is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.^[1] In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified. Antennas are essential components of all radio equipment.^[2]

An antenna is an array of conductors (elements), electrically connected to the receiver or transmitter. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally (omnidirectional antennas), or preferentially in a particular direction (directional, or high-gain, or "beam" antennas). An antenna may include components not connected to the transmitter, parabolic reflectors, horns, or parasitic elements, which serve to direct the radio waves into a beam or other desired radiation pattern. Strong directivity and good efficiency when transmitting are hard to achieve with antennas with dimensions that are much smaller than a half wavelength.

The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of waves predicted by the electromagnetic theory of James Clerk Maxwell. Hertz placed dipole antennas at the focal point of parabolic reflectors for both transmitting and receiving.^[3] Starting in 1895, Guglielmo Marconi began development of antennas practical for long-distance, wireless telegraphy, for which he received a Nobel Prize.^[4]

Half-wave dipole antenna receiving a radio wave: The electric field (E) of the incoming wave pushes the electrons in the rods back and forth, and oscillating currents (black arrows) flow through the receiver.

Antenna radiating radio waves: The transmitter applies an alternating current (red arrows) to the rods, which charges them alternately positive and negative, emitting loops of electric field. The arrows of the loops get reversed each time the current changes polarity.